Grommets have become the most common implants in the human body in recent years. The insertion of grommets has now become the most common form of operation, not only in the ENT field, but also in all branches of surgery in the North Western part of the world (Europe and the United States); that is why it is of great importance to design grommets which are better than those currently being used.
Grommets are known in many forms. In this connection reference is made to the thesis entitled "Trommelvliesbuisjes" (Grommets), W. H. Moesker, Amsterdam, 1991, which gives a general description of all kinds of grommets. Most of them are in the form of a "collar-button". They have a "waist"-shaped middle part, which makes the grommet sit securely in the eardrum after a hole has been made in the eardrum. Since the material of the eardrum is slightly elastic, it can be stretched during insertion of the grommet, and will spring back after the grommet is in its correct position.
The purpose of grommets is to provide the tympanic cavity with air, in order to relieve hardness of hearing due to moisture in the tympanic cavity as a result of little or no ventilation of the tympanic cavity. The fact that there is little or no ventilation produces partial vacuum in the tympanic cavity, with the result that fluid is sucked out of the mucous membrane lining the tympanic cavity. The tympanic cavity is thus filled with fluid (otitis media serosa), which gives rise to hardness of hearing and a greatly increased risk of ear infections. This partial vacuum occurs through the fact that the mucous membrane lining the Eustachian tube is swollen as a result of a runny nose and cold, which is particularly common in children.
The disadvantage of the current grommets is that they soon become blocked with congealed fluid, mucus or blood from the tympanic cavity, or by ear wax. They are therefore no longer able to fulfil their function of ventilation of the tympanic cavity. Besides, a grommet which is blocked is more quickly expelled through the formation of fluid and mucus in the tympanic cavity, which, as it were, pushes out the grommet.
A number of the most commonly used grommets are mentioned below, with their specific disadvantages:
The Shepard grommet. Disadvantages: The grommet quickly becomes blocked through the relatively long and straight tubular channel and the presence of a neck. As a result, the grommet is expelled relatively quickly from the eardrum. The absence of a genuine flange means that the grommet is expelled particularly quickly. Moreover, the grommet is difficult to insert with fine insertion forceps, due to the awkwardly shaped, thick top side of the grommet.
The collar-button grommet in the shape of a diabolo. This grommet also quickly becomes blocked owing to the straight, tubular channel, with the result that it too is expelled relatively quickly. The diabolo shape means that this grommet easily fits completely under the eardrum.
The "Donaldson" grommet. This grommet is more or less the same diabolo shape as the collar-button grommet, and thus has the same disadvantages. It also has another disadvantage: the small dimensions of the flange which goes under the eardrum means that this grommet remains on average an even shorter time in position than the collar-button grommet.
The LENS grommet. The relatively long neck between the flange at the bottom side and the funnel-shaped top side means that this grommet also quickly becomes blocked and is expelled as a result.
There are also many other grommets which are less often used.
If a grommet is expelled quickly from the eardrum (for example, after 6 months or sooner), there is more than a 50% chance of a recurrence of fluid accumulation in the tympanic cavity and of an ear infection occurring, which makes another insertion (generally under general anaesthetic) of a grommet necessary. If, on the other hand, a grommet remains longer in the eardrum (between one and two years), the chance of a recurrence of fluid accumulation in the tympanic cavity and of ear infections is reduced to below 50%. A grommet thus has an ideal residence time of one to two years.
The residence time of the grommet is determined by:
a. the angle which the tubular part forms with the flange which hooks under the eardrum; PA1 b. the size and shape of the flange. PA1 a. the angle between the flange and the trumpet-shaped top side is smaller than 90.degree.. PA1 b. the flange is relatively large, namely either round and the same size as the widely "fanning" top side of the trumpet-shaped top part of the grommet, or is provided with one or more symmetrical or asymmetrical "projections"; PA1 c. there is no neck, which is present in, for example, the Shepard grommet, the collar-button grommet, the Donaldson grommet and the LENS grommet.
Re: a. the angle between tubular part and flange: If this angle is small and is not acute, but is obtuse, that is to say more than 90 degrees (as in the case of the Shepard grommet), the residence time of the grommet will be short. The more acute this angle, that is to say 90.degree. or less, the longer the grommet will, as it were, remain hooked under the eardrum.
Re: b. the size and shape of the flange: If the flange is relatively small (as in the case of the Donaldson grommet), the residence time will be relatively short.
The above-mentioned grommets belong to the group of grommets which remain a relatively short time in the eardrum, from several months to many months.
In addition, there is a group of grommets which remain for a very long time in the eardrum, in general many years. The most well-known of this group is the T-drain, also called after its inventor Goode: the Goode T-drain. These grommets, which stay in the eardrum for many years, have not only the advantage of a long residence time, but also the disadvantage that their long residence time in many cases gives rise to permanent holes in the eardrum, which have to be closed surgically.
Since many millions of grommets are placed annually, slight differences (in quality) between them can have great consequences (in quantity).